LMR38010-Q1: DC-DC IC Failed

Gobi Rajagopal

Part Number: LMR38010-Q1

LMR38010FSQDDARQ1 Failure Observation

We observed failure (short circuit) of two LMR38010FSQDDARQ1 devices.

Initially, the EN pin was directly connected to the VIN pin, and the circuit operated without any issues.

Later, a Common Mode Choke (CMC) was added in the input line to improve EMI/EMC performance, and the EN pin was connected to the Ignition (IGN) input instead of the IN pin. Following this change, the LMR38010FSQDDARQ1 devices started failing and became short-circuited.

Subsequently, 47 k series resistor was added in the EN pin path, after which the circuit has been operating reliably without any failures.

Could you help identify the possible root cause of this failure?

According to the datasheet, the EN pin can withstand voltages greater than 80 V, whereas our system input voltage is only 24 V, our total load current is 60mA and DC-DC output is 13V (24V to 13V), 400KHZ SW freq

9 days ago

0 Tony Koulong 9 days ago

TI__Genius 10090 points

Hi Gobi,

Can you share your schematic and the other changes you did on the design?

0 Gobi Rajagopal 8 days ago

Prodigy 20 points

0 Gobi Rajagopal 5 days ago in reply to Gobi Rajagopal

Prodigy 20 points

I shared the Sch and but no response from your end

0 Tony Koulong 5 days ago in reply to Gobi Rajagopal

TI__Genius 10090 points

Hi Gobi,

Please allow sometime to investigate this issue.

Have you tried to tie EN to VIN with the common mode choke connected?

0 Gobi Rajagopal 4 days ago in reply to Tony Koulong

Prodigy 20 points

Yes ..it is working fine

only problem is if i connect EN pin to IGN line, then only Buck IC getting fail.
is common mode choke creating any impact?
Input voltage is 24V for Vbat and IGN line

is buck will create any differential voltage between Vbat line and IGN line?

0 Tony Koulong 4 days ago in reply to Gobi Rajagopal

TI__Genius 10090 points

Hi Gobi,

I am checking the absolute maximum rating for EN. Can you measure the transient voltage of the IGN line and make sure it does not exceed Vin + 0.3V?

I suspect that EN is seeing a higher voltage than it is supposed to, which may be due to a high surge current that quickly melts the tiny internal diode.

0 Gobi Rajagopal 3 days ago in reply to Tony Koulong

Prodigy 20 points

Already we referred the datasheet. we knew this information

Vbat = 24V
IGN = 24V

0 Tony Koulong 3 days ago in reply to Gobi Rajagopal

TI__Genius 10090 points

Hi Gobi,

Did you measure the transient voltage of IGN with the common mode choke?

My observation is that a positive transient on the IGN line spikes higher than the voltage at the VIN pin, the internal diode becomes forward biased.

Mother question would be "Without the common mode choke. Is the IC still failing while EN is tie to IGN

0 Gobi Rajagopal 3 days ago in reply to Tony Koulong

Prodigy 20 points

You mean, if Vbat = 24V and IGN = 24.4V , then EN pin s getting fail or not ? (>0.3V)

If yes , now, we added a series resistor.
(ie) IGN line --> 47K series resistor --> EN pin ..is this ok ?

0 Gobi Rajagopal 3 days ago in reply to Gobi Rajagopal

Prodigy 20 points

In datasheet,
Vin max voltage is 85V
EN max voltage is Vin + 0.3 V

Query: EN max voltage means 85 + 0.3V or 24V + 0.3V (if we apply Vin is 24V from Vbat line)
which one is correct ?

0 Tony Koulong 3 days ago in reply to Gobi Rajagopal

TI__Genius 10090 points

Hi Gobi,

Gobi Rajagopal said:
If yes , now, we added a series resistor.
(ie) IGN line --> 47K series resistor --> EN pin ..is this ok ?

Yes. The 47kΩ series resistor limits the peak transient surge current entering the EN pin, thereby preventing thermal overload and subsequent short-circuit failure of the internal ESD protection structures.

0 Tony Koulong 3 days ago in reply to Gobi Rajagopal

TI__Genius 10090 points

Hi Gobi,

Gobi Rajagopal said:
In datasheet,
Vin max voltage is 85V
EN max voltage is Vin + 0.3 V

Query: EN max voltage means 85 + 0.3V or 24V + 0.3V (if we apply Vin is 24V from Vbat line)
which one is correct ?

True about EN abs max.

For your application it is 24V+0.3V. EN voltage cannot exceed this or it would failed. This is dependent of your VIN voltage.

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LMR38010-Q1: DC-DC IC Failed